CHICAGO — Protesters vowed to carry out disruptive demonstrations Monday in Chicago, a day after baton-wielding police clashed with demonstrators in a violent confrontation that left dozens injured just blocks from where NATO leaders were gathered.

Occupy Chicago, one of the groups that helped organize the demonstrations, took to social media to urge people to join in another planned demonstration at 10 a.m. ET on Monday, the final day of the two-day NATO summit. Thousands of people have hit the streets to protest everything from the war in Afghanistan to the economy.

While some protesters accused police of brutality, Illinois Lt. Gov. Sheila Simon said Monday that police seemed to be doing a good job.

“I think for the most part, they have been doing a fantastic job of making sure that people are protected and free speech rights are protected as well,” she said. “It’s a tough balance to get, but I think they are doing a good job.”

Sunday’s clashes began at the end of a march, just blocks from the NATO summit, after a group of protesters refused police orders to disperse and began pushing against a line of police officers clad in riot gear.

A video from CNN affiliate WLS showed protesters, some with bloodied faces, struggling against the officers, some of whom used their batons to strike the demonstrators.

The confrontation led to a two-hour standoff between police and protesters before it broke up, with demonstrators heading toward the Chicago Art Institute, where first lady Michelle Obama was reportedly set to host a dinner.

While some protesters held a sit-in near the institute, others took to the streets to block traffic.

Chicago Police and Occupy Chicago both reported injuries in their ranks during the clashes earlier in the day.

Police arrested at least 45 people Sunday. Four officers were taken to the hospital with injuries, Chicago Police Superintendent Garry McCarthy said. One officer had been stabbed in the leg, he said.

“They rallied. They charged the cops and they assaulted the officers,” McCarthy said of protesters. “The finger should be pointed at the people who assaulted the cops.”

Protesters posted photos to Twitter purporting to show bloody and beaten protesters.

“The police have several demonstrators detained behind their lines, calling for medics. Bloodied protesters being dragged out of sight now,” Occupy Chicago wrote on its Twitter page earlier in the day.

Occupy Chicago said dozens were injured in the clashes, though fewer than a dozen protesters were treated at area hospitals, officials said.

McCarthy accused some protesters of splashing red paint on themselves to make it look like they had been wounded.

The protest groups said police detained more than 100 people.

A city official, who was not authorized to talk to the media on police matters, told CNN that the confrontation began when about 75 to 100 protesters refused to leave the area after being told to disperse.

They threw bottles and other objects at police, the official said.

— CNN’s Jim Spellman, Ted Rowlands, Paul Vercammon, Bill Kirkos and Katherine Wojtecki, contributed to this report.